.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" References consulted: .\" Linux libc source code .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) .\" 386BSD man pages .\" Modified Sat Jul 24 19:49:27 1993 by Rik Faith (faith@cs.unc.edu) .\" Modified Fri Apr 26 12:38:55 MET DST 1996 by Martin Schulze (joey@linux.de) .\" .TH CTIME 3 "April 26, 1996" "BSD" "Linux Programmer's Manual" .SH NAME asctime, ctime, gmtime, localtime, mktime \- transform binary date and time to ASCII .SH SYNOPSIS .nf .B #include .sp .BI "char *asctime(const struct tm *" timeptr ); .sp .BI "char *ctime(const time_t *" timep ); .sp .BI "struct tm *gmtime(const time_t *" timep ); .sp .BI "struct tm *localtime(const time_t *" timep ); .sp .BI "time_t mktime(struct tm *" timeptr ); .sp .BI "extern char *" tzname [2]; .BI "long int " timezone ; .BI "extern int " daylight ; .fi .SH DESCRIPTION The \fBctime()\fP, \fBgmtime()\fP and \fBlocaltime()\fP functions all take an argument of data type \fItime_t\fP which represents calendar time. When interpreted as an absolute time value, it represents the number of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal Time (UTC). .PP The \fBasctime()\fP and \fBmktime()\fP functions both take an argument representing broken-down time which is a binary representation separated into year, month, day, etc. Broken-down time is stored in the structure \fItm\fP which is defined in \fI\fP as follows: .sp .RS .nf .ne 12 .ta 8n 16n 32n struct tm { int tm_sec; /* seconds */ int tm_min; /* minutes */ int tm_hour; /* hours */ int tm_mday; /* day of the month */ int tm_mon; /* month */ int tm_year; /* year */ int tm_wday; /* day of the week */ int tm_yday; /* day in the year */ int tm_isdst; /* daylight saving time */ }; .ta .fi .RE .PP The members of the \fItm\fP structure are: .TP .I tm_sec The number of seconds after the minute, normally in the range 0 to 59, but can be up to 61 to allow for leap seconds. .TP .I tm_min The number of minutes after the hour, in the range 0 to 59. .TP .I tm_hour The number of hours past midnight, in the range 0 to 23. .TP .I tm_mday The day of the month, in the range 1 to 31. .TP .I tm_mon The number of months since January, in the range 0 to 11. .TP .I tm_year The number of years since 1900. .TP .I tm_wday The number of days since Sunday, in the range 0 to 6. .TP .I tm_yday The number of days since January 1, in the range 0 to 365. .TP .I tm_isdst A flag that indicates whether daylight saving time is in effect at the time described. The value is positive if daylight saving time is in effect, zero if it is not, and negative if the information is not available. .PP The \fBctime()\fP function converts the calendar time \fItimep\fP into a string of the form .sp .RS "Wed Jun 30 21:49:08 1993\\n" .RE .sp The abbreviations for the days of the week are `Sun', `Mon', `Tue', `Wed', `Thu', `Fri', and `Sat'. The abbreviations for the months are `Jan', `Feb', `Mar', `Apr', `May', `Jun', `Jul', `Aug', `Sep', `Oct', `Nov', and `Dec'. The return value points to a statically allocated string which might be overwritten by subsequent calls to any of the date and time functions. The function also sets the external variable \fItzname\fP with information about the current time zone. .PP The \fBgmtime()\fP function converts the calendar time \fItimep\fP to broken-down time representation, expressed in Coordinated Universal Time (UTC). .PP The \fBlocaltime()\fP function converts the calendar time \fItimep\fP to broken-time representation, expressed relative to the user's specified time zone. The function sets the external variables \fItzname\fP with information about the current time zone, \fItimezone\fP with the difference between Coordinated Universal Time (UTC) and local standard time in seconds, and \fIdaylight\fP to a non-zero value if standard US daylight savings time rules apply. .PP The \fBasctime()\fP function converts the broken-down time value \fItimeptr\fP into a string with the same format as \fBctime()\fP. The return value points to a statically allocated string which might be overwritten by subsequent calls to any of the date and time functions. .PP The \fBmktime()\fP function converts a broken-down time structure, expressed as local time, to calendar time representation. The function ignores the specified contents of the structure members \fItm_wday\fP and \fItm_yday\fP and recomputes them from the other information in the broken-down time structure. Calling \fBmktime()\fP also sets the external variable \fItzname\fP with information about the current time zone. If the specified broken-down time cannot be represented as calendar time, \fBmktime()\fP returns a value of (time_t)(\-1) and does not alter the \fItm_wday\fP and \fItm_yday\fP members of the broken-down time structure. .SH "CONFORMING TO" SVID 3, POSIX, BSD 4.3, ISO 9899 .SH "SEE ALSO" .BR date "(1), " gettimeofday "(2), " time "(2), " tzset (3), .BR difftime (3), .BR strftime (3), .BR newctime (3).